Frolicking chimp youngsters spread deadly epidemics

Child’s play among wild chimpanzees may spread deadly outbreaks to the rest of the family.

A 22-year study of respiratory disease epidemics among chimps has found that death and disease spikes when numerous chimps neared 2 and a half years old – the age at which young apes frolic the most.

“Chimps pull hair and roll together, but then afterwards they come back to the mother,” says Christophe Boesch, a primatologist at Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was involved in the study.

Such cycles mimic schoolyard epidemics in children. “We all know that when kids are of a certain age they will come back with a flu and all the family will get it,” Boesch says.

Advertisement

Death records

Vaccinating young chimpanzees and limiting contact with humans – from whom they can catch deadly diseases – might help stem these outbreaks, says Peter Walsh from the Max Planck Institute for Evolutionary Anthropology, who was also involved in the study.

Boesch’s team began studying chimpanzees living in Taï National Park in Côte d’Ivoire in the late 1970s, garnering insight into tool use, hunting practices and the day-to-day lives of the animals. His team also kept detailed logs of births, deaths, and disease in two separate groups comprising 250 animals.

To see what factors might drive such epidemics, Boesch, Walsh and colleague Hjalmar Kühl plotted the chimp deaths on a timeline and looked for natural cycles with a similar pattern. They expected that a weather phenomenon such as El Niño would explain the outbreaks.

Age cycle

Instead, the primatologists noticed that epidemics flared up every three and a half years, right when a batch of chimps reached their most rambunctious age.

Infants of all ages died in each outbreak, and their mothers responded by getting pregnant and delivering about a year later. This produced a batch of children all about the same age.

When those children hit 2 to 2 and half years of age, they play twice as long and with twice as many peers, compared with older and younger apes. The increased contact spreads disease and foments another epidemic.

That conclusion relies on some circumstantial evidence and assumptions, but seems likely, says Elizabeth Lonsdorf at the Lincoln Park Zoo in Chicago. “If they were building a lawyer’s case, it would look pretty convincing,” she adds.

Knee-jerk reactions

However, not all chimpanzee populations have the same social dynamics, she says. The apes she studies in Tanzania do not give birth in sync, and mothers of young children tend to isolate themselves and their offspring.

“It used to be that a chimp was a chimp. Now that many more studies have been done, we know that that is not always the case,” she says.

Since stopping chimpanzees from playing isn’t an option, the researchers say they and other humans should steer clear from the chimps when a cohort of youngsters nears two and half.

Targeted vaccination of playful infants and other chimpanzees might also cut down on disease transmission, an idea that could stir up controversy in the hands-off world of animal conservation, Walsh says.

“The problem is that some elements of conservation community just have knee-jerk reactions against aggressive management,” he says. “They only see stress to animals, but can’t seem to factor in the huge population impact of doing nothing.”